This invention relates to rigid polyurethane modified polyisocyanurate foams, particularly highly filled foams containing fly ash an an inorganic filler.
Rigid polyurethane and polyisocyanurate foams are widely used as structural members, and particularly as insulative structural members. As with other polymeric materials, it is often desirable to reduce the polymer content and improve the properties of these members by the addition of inorganic fillers. Unfortunately, it has proven difficult to provide a rigid polyurethane or polyisocyanurate foam containing more than about 10% by weight of such fillers. These fillers tend to rupture the cells of the foam, which in turn dramatically reduces its insulative capacity. Another undesirable effect of high levels of fillers is that they cause the foam to be very friable. Since higher filler levels are desired because they provide a less expensive material and certain physical property improvements, it would be highly desirable to provide a highly filled, rigid polyurethane-modified polyisocyanurate foam which has good insulative properties and low friability.